The ASTM D7887-2020 Standard Guidance provides systematic guidance for the selection of non-hazardous liquid alternatives for United Nations Encasement performance testing. The guidance is designed to ensure conformity and repeatability of test results when alternative liquid filler materials are used, reducing discrepancies in test results due to inconsistent material selection. By standardizing the physical characterization of filler materials, this guidance helps Encasement manufacturers and testing laboratories develop standards-compliant test plans that enhance confidence in Encasement designs and improve transportation safety. The guidance also provides specific information related to United Nations certification testing and provides clear guidance on the selection of test filler materials.